Organic EL is a self-emissive element which is capable of high contrast display and has fast response speed. For this reason, there is a high expectation for application as a next generation display which can display high-quality images. Organic EL element is sometimes driven by passive matrix, but active matrix type which uses a thin-film transistor (TFT) that is advantageous in producing high resolution is becoming popular in recent years. A display is produced using high quality thin-film transistor (TFT) such as low-temperature polysilicon to continuously drive organic EL element for long hours, but it is considered difficult under present circumstances to produce a display in a larger size at low cost because the production cost of low-temperature polysilicon is high. Thus, low-temperature polysilicon is put into a practical use mainly for a small size.
On the other hand, low temperature silicon TFT has a high mobility and long stability behavior, and can be used not only for pixels but also for driving circuit which behaves at a high speed. Therefore, a driving circuit (driver) for driving a select line or a data line is formed on a same glass substrate as pixels to omit a part of an electronic component such as a driver IC for an overall cost reduction.
However, lower-temperature polysilicon TFT has significantly variable Vth (threshold) and mobility characteristics. Thus, when TFT which drives organic EL is used in a saturated region (constant current drive), it is common to introduce a correction circuit within pixels. For example, as it is disclosed in patent reference 1, non-uniform display due to differences in characteristics of driving transistor can be improved by correcting Vth of driving transistor using a plurality of transistor.